Laser irradiating method and device for same

ABSTRACT

Because a focal distance of a condenser lens is changed due to a change in temperature, when irradiation of a laser beam is restarted after the irradiation has stopped, it takes a long time to restore a temperature of the cooled lens to a given temperature, and the operating efficiency is deteriorated. A first mirror  5  that can be located at a reflection position I at which an optical path is blocked and a laser beam a is reflected, and a second mirror  6  that reflects the laser beam a which is reflected by the first mirror  5  are disposed between the condenser lens  2  and the object to be irradiated  4 . The first mirror  5  is located at the reflection position I so that the laser beam a that is transmitted through the condenser lens  2  is sequentially reflected by the first and second mirrors  5  and  6 , and an intensity of the laser beam a that is again reflected by the first mirror  5  is made to coincide with an intensity of the laser beam a that is reflected from the object to be irradiated  4 , and the condenser lens  2  is heated in the same manner that the processing laser beam a is transmitted through the condenser lens  2  and irradiated on the object to be irradiated  4.

TECHNICAL FIELD

The present invention relates to a laser irradiating method and a devicefor the method, and more particularly, to a laser irradiating method ofcondensing or focusing a laser beam from a laser oscillator through alens, and irradiating an object to be irradiated which is mounted on astage with the laser beam to reform the object to be irradiated, and adevice for the method, which have a mirror for maintaining a temperatureof the lens and also a focal distance.

BACKGROUND ART

Up to now, in manufacture of crystallized silicon of a thin filmtransistor, an object to be irradiated having a thin a—Si (amorphoussilicon) film formed on a glass substrate is irradiated with a laserbeam, and the a—Si film is crystallized to provide a p—Si (polysilicon)film. As one of methods of irradiating the a—Si film with a laser beamto reform the a—Si film, there is a method in which a laser beam havinga uniform intensity is applied to a mask, and the laser beam is thenprojected and focused on the a—Si film of the object to be irradiated bymeans of a condenser lens of an optical device. Thus, the object isirradiated with the laser beam (for example, Patent Document 1).

In the method, a laser beam that is produced by a laser oscillator thatgenerates an excimer laser beam is introduced into the optical device,and appropriately diverted by means of a reflective mirror, and theintensity of the laser beam is equalized. After that, the laser beam isallowed to pass through the mask and the condenser lens so as to beshaped in a square line beam (pulse laser beam), and then condensed andtransferred to the object to be irradiated. The object to be irradiatedis located within a vacuum chamber of a laser beam anneal device.

Patent Document 1: JP 3204986 B

DISCLOSURE OF THE INVENTION

Problem to be Solved by the Invention

However, the conventional laser irradiating device as described abovesuffers from a technical problem in that a focal distance of the lensfluctuates due to a change in temperature. That is, because the pulselaser beam that is produced by the laser oscillator is allowed to passthrough the condenser lens, and then irradiated to the object to beirradiated, a part of laser beam is absorbed by the lens and transformedinto a heat to increase the temperature of the lens when the laser beampasses through the condenser lens. The temperature of the lens isgenerally maintained to a given temperature to prevent a change in focaldistance. When an irradiation is restarted after the successiveirradiation of the pulse laser beam stops, there is required a long timeto restore the temperature of the lens which has been cooled once to agiven temperature, which causes deterioration of the operatingefficiency.

In order to prevent a change in the focal distance that is attributableto the change in the temperature, the condenser lens is housed in a lenstube, the condenser lens is indirectly heat-insulated by the aid of atemperature control device that is attached to the lens tube, and thetemperature of the lens is maintained to a given temperature. In thiscase, the lens is mainly directly heated by the laser beam to increasethe temperature. On the other hand, the temperature control of the lensis indirectly conducted from the side surface. For this reason, a timeconstant of the temperature rise of the lens by the laser beam isshorter than the time constant of cooling by the temperature controldevice. Therefore, when the laser beam irradiation is restarted afterthe successive irradiation of the pulse laser beam has been stopped, thelens temperature rises in a short period of time, then drops, and isthereafter stabilized. Because the focal distance of the lens continuesto change until the temperature has been stabilized, the object to beirradiated is irradiated with the laser beam out of focus.

Also, in order to suppress a change in the focal distance which isattributable to the change in the temperature of the condenser lens, anattempt is made to combine lenses made of a plurality of materials thatare different in temperature characteristic with each other. However,the suppression effect is insufficient.

Means for Solving the Problem

The present invention has been made in view of the above-mentionedconventional technical problems, and a configuration of the presentinvention will be described below.

An invention of claim 1 provides a laser irradiating method ofcondensing or focusing a processing laser beam a from a laser oscillator1 through a lens 2, and irradiating an object to be irradiated 4 withthe processing laser beam a, in which a first mirror 5 that can belocated at a reflection position I at which an optical path between thelens 2 and the object to be irradiated 4 is blocked and the processinglaser beam a with a given reflectivity is reflected and at an openposition II at which the optical path between the lens 2 and the objectto be irradiated 4 is opened is arranged between the lens 2 and theobject to be irradiated 4, and a second mirror 6 that reflects theprocessing laser beam a with a given reflectivity is arrangedperpendicularly to an optical axis L of the processing laser beam awhich is reflected by the first mirror 5 located at the reflectionposition I, and the first mirror 5 is located at the reflection positionI so that the processing laser beam a that is transmitted through thelens 2 is sequentially reflected by the first mirror 5 and the secondmirror 6, and an intensity of the processing laser beam a that is againreflected by the first mirror 5 is made to coincide with an intensity ofthe processing laser beam a that is reflected from the object to beirradiated 4 in a state where the first mirror 5 is located at the openposition II, and the lens 2 is heated in the same manner that theprocessing laser beam a is transmitted through the lens 2, andirradiated on the object to be irradiated 4.

An invention of claim 2 provides a laser irradiating device forcondensing or focusing a processing laser beam a from a laser oscillator1 through a lens 2, and irradiating an object to be irradiated 4 withthe processing laser beam a, in which a first mirror 5 that can belocated at a reflection position I at which an optical path between thelens 2 and the object to be irradiated 4 is blocked and the processinglaser beam a with a given reflectivity is reflected and at an openposition II at which the optical path between the lens 2 and the objectto be irradiated 4 is opened is arranged between the lens 2 and theobject to be irradiated 4, and a second mirror 6 that reflects theprocessing laser beam a with a given reflectivity is arrangedperpendicularly to an optical axis L of the processing laser beam awhich is reflected by the first mirror 5 located at the reflectionposition I, and the first mirror 5 is located at the reflection positionI so that the processing laser beam a that is transmitted through thelens 2 is sequentially reflected by the first mirror 5 and the secondmirror 6, and an intensity of the processing laser beam a that is againreflected by the first mirror 5 is made to coincide with an intensity ofthe processing laser beam a that is reflected from the object to beirradiated 4 in a state where the first mirror 5 is located at the openposition II, and the lens 2 is heated in the same manner that theprocessing laser beam a is transmitted through the lens 2 and irradiatedon the object to be irradiated 4.

An invention of claim 3 provides the laser irradiating device accordingto claim 2, in which the first mirror 5 is made of a total reflectionmirror, the second mirror 6 is made of a half mirror having the samereflectivity as the reflectivity of the object to be irradiated 4, andthe second mirror 6 is located at a position apart from the first mirror5 by a distance h1 that is equal to a distance h2 between the firstmirror 5 and the object to be irradiated 4.

An invention of claim 4 provides the laser irradiating device accordingto claim 2 or 3, in which the lens 2 includes measuring means 7 formeasuring the focal distance.

An invention of claim 5 is the laser irradiating device according to anyone of claims 2 to 4, in which the lens 2 is attached with a temperaturecontrol device 3.

EFFECT OF THE INVENTION

According to the inventions of independent claims 1 and 2, thetemperature of the lens is stabilized without irradiating the object tobe irradiated with a processing laser beam, so the focal distance of thelens can be prevented from changing due to the change in thetemperature, thereby making it possible to always keep the quality ofthe laser beam with which the object to be irradiated is irradiatedconstant. As a result, the defocused laser beam is prevented from beingapplied to the object to be irradiated in an initial stage of startingthe irradiation of the object to be irradiated with the processing laserbeam, and only the object to be irradiated with a high quality can bemanufactured without any waste of the object to be irradiated.

More particularly, a first mirror is located at a reflection positionsince the processing of one object to be irradiated has been completeduntil a subsequent object to be irradiated is set, thereby making itpossible to keep the temperature of the lens and the focal distanceconstant.

According to claim 3, the intensity of the processing laser beam whichis again reflected by the first mirror is made to coincide with theintensity of the processing laser beam which is reflected from theobject to be irradiated in a state where the first mirror is located atthe open position. As a result, it is possible to readily realize thatthe lens is heated similarly when the object to be irradiated isirradiated with the processing laser beam through the lens.

According to claim 4, there is provided measuring means for measuringthe local distance of the lens, so it is possible to measure whether thetemperature of the lens is in a desired state or not.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view showing a laser irradiating device according toone embodiment of the present invention.

FIG. 2 is a back view specifically showing measuring means that isequipped in the laser irradiating device.

FIGS. 3E to 3G are diagrams each showing a waveform of a laser beam forfocal distance measurement which is received by a measuring equipment,respectively.

BEST MODE FOR CARRYING OUT THE INVENTION

An object of the present invention is to provide a laser irradiatingmethod of condensing or focusing a laser beam and irradiating an objectto be irradiated with the laser beam which is located on a stage througha lens to reform the object to be irradiated and a device for themethod, which include a mirror for maintaining the temperature of a lensas well as a focal distance, keep the quality of the laser beamconstant, and manufacture only an object to be irradiated with a highquality.

Embodiments

FIGS. 1 to 3 show a laser irradiating device having a mirror formaintaining a focal distance of a condenser lens (lens) according to oneembodiment of the present invention. Referring to FIG. 1, referencenumeral 1 denotes a laser oscillator, and a processing pulse laser beama (wavelength: for example, 308 nm) from the laser oscillator 1 isshifted by 90 degrees by a mirror 10 that totally reflects theprocessing laser beam a, and guided to a condenser lens 2. The laserbeam a that has passed through the condenser lens 2 is condensed (orfocused) and irradiated onto an object to be irradiated 4 to subject theobject to be irradiated 4 to crystallization. The laser beam a isactually allowed to pass through a mask (not shown) or the like so as tobe converted into a square laser beam that is shaped and equalized inintensity, and then focused on the object to be irradiated 4. Thecondenser lens 2 is received in a lens tube 16, and is indirectly cooledor heated by a temperature control device 3 that is made of a Peltierdevice attached to the outer side of the mirror tube 16 so as tomaintain a given temperature of the lens.

The object to be irradiated 4 is mounted on a stage 11, and a movingdevice 12 is attached to the stage 11. The moving device 12 is caused torelatively move the stage 11 with respect to the laser oscillator in agiven direction X. With this configuration, the object to be irradiated4 which is mounted on the stage 11 is irradiated with the laser beam aat given intervals to reform the object to be irradiated 4.

A first mirror 5 (reflective mirror) which reflects the processing laserbeam a with a given reflectivity can be arranged between the condenserlens 2 and the object to be irradiated 4. The mirror 5 is capable ofblocking an optical path between the condenser lens 2 and the object tobe irradiated 4. The mirror 5 is driven by a drive device 14 so as to belocated at a reflection position I (indicated by a solid line) whichblocks the optical path between the condenser lens 2 and the object tobe irradiated 4, and an open position II (indicated by a virtual line)which opens the optical path between the condenser lens 2 and the objectto be irradiated 4. The mirror 5 is normally made of a total reflectionmirror. In this case, the mirror 5 is located at the reflection positionI so as to function as an optical shutter that blocks the processinglaser beam a which is directed toward the stage 11. Even when theoptical path is closed by the optical shutter, the processing laser beama passes through the condenser lens 2.

Also, a second mirror 6 that reflects the processing laser beam a with agiven reflectivity is arranged. The mirror 6 is disposed perpendicularlyto an optical axis L of the processing laser beam a that is reflected bythe first mirror 5 which is located at the reflection position I. Adistance h1 of the mirror 6 from the first mirror 5 is set to be equalto a distance h2 between the first mirror 5 and the object to beirradiated 4. The second mirror 6 is normally made of a half mirror, andhas a reflectivity (about 60%) identical with the reflectivity of theobject to be irradiated 4. The second mirror 6 is attached to a damper17 that absorbs the transmitted processing laser beam a.

In addition, the laser irradiating device further includes measuringmeans 7 for measuring a focal distance of the condenser lens 2. In themeasuring means 7, more specifically, as shown in FIG. 2, after a focaldistance measurement laser beam b (wavelength: for example, 635 nm) isallowed to pass through a cylindrical lens 21, the focal distancemeasurement laser beam b is reflected by a reflection mirror 22 which ismade of a half mirror so as to be diverted. Also, the focal distancemeasurement laser beam b is allowed to pass through a mirror 10,condensed through the condenser lens 2, and allowed to pass through thefirst mirror 5 so as to be irradiated onto the surface of the object tobe irradiated 4. The reflected light from the object to be irradiated 4is allowed to sequentially pass through the first mirror 5, thecondenser lens 2, and the mirrors 10 and 22, and then received by ameasuring device 24. Accordingly, the mirror 10 and the first mirror 5are capable of totally reflecting the processing laser beam a, buttransmit the focal distance measurement laser beam b.

It can be determined whether a distance on the optical path between thecondenser lens 2 and the object to be irradiated 4 as well as the focaldistance of the condenser lens 2 is adequate or not, on the basis of theconfiguration of the beam b that has been received by the measuringdevice 24. The focal distance of the condenser lens 2 is measured as adifference B-A of the distance on the optical axis between the condenserlens 2 and the object to be measured 4. The configuration of the beamthat is received by the measuring device 24 is shown in FIGS. 3(E) to3(G). FIG. 3(E) shows a too longer focal distance of the condenser lens2, FIG. 3(F) shows an appropriate state, and FIG. 3(G) shows a tooshorter focal distance of the condenser lens 2.

Now, the operation will be described.

The processing pulse laser beam a from the laser oscillator 1 isdiverted by 90 degrees by means of the total reflection mirror 10, andguided to the condenser lens 2. The laser beam a that is transmittedthrough the condenser lens 2 is conversed and irradiated onto the objectto be irradiated 4 to reform the object to be irradiated 4. When theobject to be irradiated 4 has a thin a—Si film formed on a glasssubstrate, the a—Si film is crystallized by irradiation of the laserbeam a to be reformed to be a thin p—Si film. In this situation, thefirst mirror 5 is located at the open position II at which the opticalpath between the condenser lens 2 and the object to be irradiated 4 isopened.

Upon completion of the irradiation processing of the laser beam a withrespect to the single object to be irradiated 4, the object to beirradiated 4 on the stage 11 is replaced with a new object to beirradiated 4. In this situation, the first mirror 5 (reflection mirror)is driven by the drive device 14 so as to be located at the reflectionposition I that blocks the optical path between the condenser lens 2 andthe object to be irradiated 4 and reflects the processing laser beam awith a given reflectivity.

With this configuration, the processing pulse laser beam a that istransmitted through the condenser lens 2 is reflected by the firstmirror 5 that is located at the reflection position I, and madeperpendicularly incident on and partially reflected by the second mirror6. The processing pulse laser beam a is reflected by the first mirror 5again, and is transmitted through the condenser lens 2. Accordingly, theintensity of the laser beam a that is reflected by the first mirror 5toward the condenser lens 2 is made to coincide with the intensity ofthe laser beam a that is reflected from the object to be irradiated 4.This heats the condenser lens 2 as in the case where the object to beirradiated 4 is irradiated with the laser beam a, and prevents avariation in the focal distance which is attributable to the cooling ofthe condenser lens 2. It is desirable that the processing laser beam athat is transmitted through the first mirror 5 does not influence thereformation processing of the object to be irradiated 4.

In particular, when the first mirror 5 is configured by a totalreflection mirror, the second mirror 6 is located at a position that isapart from the laser beam a by the distance h1 that is equal to thedistance h2 between the first mirror 5 and the object to be irradiated4. Also, the reflectivity of the second mirror 6 is made equal to thereflectivity of the object to be irradiated 4, thereby making itpossible that the intensity of the laser beam a which is reflected fromthe first mirror 5 toward the condenser lens 2 readily coincides withthe intensity of the pulse laser beam a that is reflected from theobject to be irradiated 4.

The first mirror 5 may not necessarily be located at the reflectionposition I only in a case of replacing the object to be irradiated 4.The case where the first mirror 5 is located at the reflection positionI widely includes a case in which there is the necessity of maintainingthe temperature of the condenser lens 2 when the object to be irradiated4 has been removed from the stage 11.

Also, as in the case where the processing laser beam a is guided to theobject to be irradiated 4, in order to receive the condenser lens 2 inthe mirror tube 16, cool the condenser lens 2 by the temperature controldevice 3 that is attached to the mirror tube 16, and maintain a giventemperature of the lens 2, the lens 2 is directly heated by the laserbeam a to increase the lens temperature whereas the temperature controlof the lens 2 is indirectly conducted from the side surface thereof. Thetemperature control device 3 can be omitted, and in the case where thetemperature control device 3 is omitted, the irradiation of the objectto be irradiated 4 with the processing laser beam a can be started in astate where the condenser lens 2 is heated by the processing laser beama and the temperature rise then stops.

The measuring means 7 for measuring the focal distance of the condenserlens 2 irradiates the surface of the object to be irradiated 4 with thefocal distance measurement laser beam b, allows the reflected light bfrom the surface to pass through the condenser lens 2 and the mirrors 5,10, and 22, and allows the focal distance measurement laser beam b to bereceived by the measuring unit 24. As a result, it is possible to knowthat the focal distance of the condenser lens 2 is in an appropriatestate on the basis of the configuration of the laser beam b that hasbeen received by the measuring device 24. It is possible to know thatthe temperature of the condenser lens 2 is appropriate on the basis ofthe fact that the focal distance of the condenser lens 2 is appropriate.

A laser oscillator LS2000 made of Lambda Physik Co., Ltd. is used as thelaser oscillator 1 to actually oscillate the processing laser beam a(308 nm in wavelength, 300 Hz in repetitive oscillation), and the firstmirror 5 resulting from depositing a dielectric multi-layer film thattotally reflects the laser beam a on quartz is located between thecondenser lens 2 and the object to be irradiated 4 with an inclinationof 45 degrees with respect to the optical axis. The first mirror 5 iscapable of transmitting a diode laser beam having a wavelength of 635 nmwhich is the focal distance measurement laser beam b.

The second mirror 6 that is formed of a half mirror is located at thedistance h1 which is equal to the distance h2 between the first mirror 5and the object to be irradiated 4 in the travel direction of theprocessing laser beam a which is reflected by the first mirror 5. Thesecond mirror 6 is located perpendicularly to the optical axis L that isbent 90 degrees by the first mirror 5.

The second mirror 6 has a reflectivity of 60% with respect to the light(processing laser beam a) that is 308 nm in wavelength, which is madeequal to the reflectivity of the substrate obtained by depositingamorphous silicon having a thickness of 50 nm which is the object to beirradiated 4 on a glass plate that is 0.5 mm in thickness with respectto the beam a of 308 nm in wavelength.

Also, the laser irradiating device also includes the measuring means 7that irradiates the object to be irradiated 4 with the beam that is 635nm in wavelength (focal distance measurement laser beam b) beyond themirror 5, and measures the focal distance of the condenser lens 2 by theaid of the reflected beam b.

The Peltier device (temperature control device 3) is located outside ofthe mirror tube 16 of the condenser lens 2 to control the temperature ofthe lens 2.

With the laser irradiating device as described above, it is confirmedthat the temperature of the condenser lens 2 can be kept substantiallyconstant by the first and second mirrors 5 and 6.

1. A laser irradiating device for condensing or focusing a processinglaser beam (a) from a laser oscillator through a lens, and irradiatingan object to be irradiated with the processing laser beam (a), wherein afirst mirror is located at a reflection position (I) at which an opticalpath between the lens and the object to be irradiated is blocked and theprocessing laser beam (a) with a given reflectivity is reflected and atan open position (II) at which the optical path between the lens and theobject to be irradiated is opened is arranged between the lens and theobject to be irradiated, and a second mirror that reflects theprocessing laser beam (a) with a given reflectivity is arrangedperpendicularly to an optical axis (L) of the processing laser beam (a)which is reflected by the first mirror located at the reflectionposition (I), and wherein the first mirror is located at the reflectionposition (I) so that the processing laser beam (a) that is transmittedthrough the lens is sequentially reflected by the first mirror and thesecond mirror, and an intensity of the processing laser beam (a) that isagain reflected by the first mirror is made to coincide with anintensity of the processing laser beam (a) that is reflected from theobject to be irradiated in a state where the first mirror is located atthe open position (II), and the lens is heated when the processing laserbeam (a) is transmitted through the lens and irradiated on the object tobe irradiated.
 2. The laser irradiating device according to claim 1,wherein the first mirror is made of a total reflection mirror, thesecond mirror is made of a half mirror having the same reflectivity asthe reflectivity of the object to be irradiated, and the second mirroris located at a position apart from the first mirror by a distance (h1)that is equal to a distance (h2) between the first mirror and the objectto be irradiated.
 3. The laser irradiating device according to claim 1,wherein the lens includes measuring means for measuring the focaldistance.
 4. The laser irradiating device according to claim 1, whereinthe lens is attached with a temperature control device.
 5. The laserirradiating device according to claim 2, wherein the lens includesmeasuring means for measuring the focal distance.
 6. The laserirradiating device according to claim 2, wherein the lens is attachedwith a temperature control device.
 7. The laser irradiating deviceaccording to claim 3, wherein the lens is attached with a temperaturecontrol device.